The current, “standard” state-of-the-art personal computer (“PC”) architecture has evolved, and continues to evolve, in response to the marketplaces demand for faster processing speeds and the quickest possible application response times. This is especially true for graphics and video intensive applications, such as, high-resolution graphic video games and streaming video programs. In addition, future processor designs that are currently being developed (for example, processors having integrated graphics co-processors), will operate at speeds far above existing bus transmission speeds. As a result, the demand for ever faster systems continues to grow. As in the past, a major limiting factor on how fast PCs can process and display information depends on how quickly the necessary information can be provided to and received from the central processor unit (“CPU”). The two major components that determine this response time are the speed of the random access memory (“RAM”) and the speed at which the bus can transmit the information in RAM to and from the CPU.
FIG. 1 is a generic block diagram of a hypothetical general PC architecture. In FIG. 1, a CPU 10 is coupled to a controller chip known as a “Northbridge” chip 20 by a front-side bus (“FSB”) 12 and the CPU 10 is also coupled to a level 2 cache RAM 50 by a back-side bus (“BSB”) 14. Integrated in the CPU 10 is a level 1 cache RAM (not shown) that can transfer data at clock speeds equivalent to the CPU 10. The “Northbridge” chip 20 is a Very Large Scale Integration (“VLSI”) chip 20 that provides the main system logic chip portion of the PC motherboard chipset 16. The “chipset” 16 couples and controls all of the different parts of the PC motherboard and usually comprises the Northbridge chip 20 and a Southbridge chip 30. The Northbridge chip 20 couples the FSB 12 from the CPU 10 to an Accelerated Graphics Port (“AGP”) bus 62 via an AGP (not shown), Intel AGP Interface Specification Revision 2.0, published May 4, 1998; a main memory bus 42; a Peripheral Component Interconnect (“PCI”) bus 82, PCI Special Interest Group (SIG) PCI Specification, Revision 20, published May 8, 1996; and a Small Computer Systems Interface (“SCSI”) bus 72, ANSI X3.131-1994, Small Computer System Interface-2 (SCSI-2), published 1994. The graphics processor 60 is also coupled to a video monitor 64 by cable 66 and the graphics processor 60 is designed to provide rapid updates of the information that is displayed on video monitor 64. The AGP bus 62 is also coupled to an AGP graphics processor 60. The graphics processor 60 can, also, coupled to a video frame buffer RAM (not shown) by a video bus (not shown) for increased display speed. Finally, the Southbridge chip 30 is coupled to the PCI bus 82 by a stub 83 for communicating with the Northbridge chip 20 and a PCI-to-PCI bridge 80.
The “Southbridge” chip 30, which is also a VLSI chip, provides connections to current and old peripheral and communication devices and cards (not shown) including, but not limited to, for example, printers, modems, keyboards, mouses, CD-ROM drives, hard disk drives, floppy disk drives and Industry Standard Architecture (“ISA”) cards. Additionally, the Southbridge chip 30 provides the interfaces for Universal Serial Bus (“USB”) connectors (not shown), USB Specification, Version 1.1, published Sep. 23, 1998 and IEEE 1394 (also referred to as “Firewire”) connectors (not shown), IEEE Standard 1394-1995, Standard for a High Performance Serial Bus, published 1995.
FIG. 2 is a generic block diagram of a hypothetical state-of-the-art PC architecture that is very similar to the architecture in FIG. 1. In FIG. 2, the only differences from FIG. 1 occur in the chipset and, specifically, on how the Northbridge chip 20 and the Southbridge chip 30 are coupled to each other and on how the chipset 16 is coupled to the PCI bus 82. In FIG. 2, the Northbridge chip 20 is now directly coupled to the Southbridge chip 30 by a proprietary bus 84 and the Southbridge chip 30 is directly coupled to the PCI bus 82 for communication over the PCI-to-PCI bridge 80.
Unfortunately, current bus speeds are not keeping pace with the advances in processor speed and, as a result, the buses are becoming a major limiting factor in overall computer system speed and performance.
Since future system and processor designs (for example, multi-processor systems and processors having integrated graphics co-processors) will operate at speeds far above existing bus transmission speeds, the demand for ever faster bus systems will continue to grow. Therefore, it can be appreciated that a substantial need exists for a new fast, high bandwidth bus that is protocol independent and can couple multiple agents.